2018 Beaches Water Quality Report Card

On Sunday, May 26, 2019, the environmental advocacy organization Save
the Harbor/Save the Bay released their annual Metropolitan Beaches Water
Quality Report Card, just in time for Memorial Day.

In 2018, weekly water quality testing at Boston’s regional beaches
began May 24th. Supplemental daily testing of Constitution Beach,
King’s Beach, Malibu Beach, Tenean Beach, and Wollaston Beach began on June
7th, 2018. Testing concluded on Labor Day weekend, September 3, 2018.

These scores reflect the percent of samples that complied with the
Massachusetts Department of Public Health’s single sample limit for bacteria
which is the most straightforward way of evaluating beach water quality and
potential impacts on human health.

In 2018, the overall water quality safety rating for Boston
Harbor’s regional beaches was 95%, a slight improvement over the 2017 score of
94%.

M Street Beach in South Boston topped the list again this year, while
Tenean Beach in Dorchester and King’s Beach in Lynn and Swampscott were the
lowest-scoring beaches in the region again in 2018.

It is important to note that the Boston Water and Sewer Commission
continues to identify and address illicit connections that contribute to the
problems at Tenean Beach in Dorchester, while both Lynn and Swampscott have
planned improvements to their sewer and storm water systems, which we expect
will result in improvement in water quality on King’s Beach upon completion.

Though 2018 was the wettest year on record for Massachusetts, with 61
inches of rain, more than 16 inches above the 20th century average
and the total rainfall during the 2018 sampling season was very similar to
2017, though more than double than in 2016.

There were several large rain events during the 2018 swimming season,
three of which were greater than 1 inch – they were 1.16, 2.68, and 1.38 inches
respectively. While the average daily rainfall for the summer was 0.12 inches,
more than 42% of the rain came in just three storms. This may indicate that the
distribution, frequency, and intensity of summer storms that seemed somewhat
atypical, may be increasingly common in the future.

Changes in the intensity and frequency of summer storms often
explains the variations we see on our beaches from year to year. These seasonal
variations are why Save the Harbor/Save the Bay is reluctant to draw
conclusions from a single year’s sampling results, preferring to rely on the
six-year average we have included in this report.

One critical weakness of our beach posting and flagging program,
where bacteria testing triggers advisories, is that postings are always a day
late because beach managers must wait 24 to 36 hours after a sample is
collected to obtain test results. Beach water quality may have already
changed significantly during this period, and the prior day’s test does not
necessarily reflect current conditions.

Instead of
relying on postings and flags, we urge beach goers to rely on common sense and
the six-year average for their beach, though we understand why it’s interesting
to see where water quality improved or declined versus the previous year.

BEACH WATER QUALITY EVALUATION METHODS AND METRICS

Save the Harbor uses quantitative metrics for assessing beach water
quality and management at the Boston Harbor region beaches. Enterococcusis the current microbial
indicator of GI illness used in marine waters, as established by EPA
guidelines. To assess and compare the water quality and conditions on each
beach, we looked at the percentage of test samples exceeding the state swimming
standard of 104 colony forming units (cfu) of Enterococcus in
100 milliliters (mL) of water.

Another indicator of water quality is the geometric mean (GM). The GM
indicates the central tendency of a set of numbers from the product of their
values and is a useful measure when values can increase exponentially, like
bacteria counts. Massachusetts Department of Health requires DCR to calculate
the GM based on bacterial exceedance values from the previous five days without
rain. A GM of 35 cfu/100 ml or greater is the threshold used to indicate
increased public health risk by EPA and will cause a beach to be flagged with a
swimming advisory.

Beaches have varying number of sampling locations, depending on beach
size; some have only one location whereas others have as many as four. The
frequency that beaches are sampled and tested for bacteria also varies by
beach, with some tested weekly and others tested daily during the swimming
season. These variations in testing frequency and number of sampling sites
affect how beach safety is calculated.

The “Primary Beach Safety” measure provided in this report calculates
the percent of samples at each beach that comply with the single sample
bacteria limit for swimming. It provides a straightforward method to
compare water quality at Boston Harbor beaches. However, this measure
does not always correspond directly with the percent of time that a beach is
actually posted with swimming advisory due to precautionary postings after rain
events, or failure to comply with the multi-day geometric mean limit described
above.

Using water quality data from the 2018 season and the previous six
years, Save the Harbor/Save the Bay has compiled this report to help the
region’s residents and visitors make informed decisions about where and when to
swim.

POPULAR CATEGORY

The South Boston community is rooted in its tradition, guided by its values and defined by its people. South Boston Today presents to you its inaugural edition with a commitment to upholding the South Boston community’s traditions, promoting its values and embracing all of its people.